"Bob H" wrote in message
...
I can't answer all your "why's" but I can say if they are little black
hard
spots that move when you touch them they are in fact aphids....they will
kill your plants left untreated, there a couple of treatments that will
kill
them and not your fish one has mint the other crushed eggshells....I don't
recall the name at this moment but I suspect a google search for aquatic
aphids will find something.
snip

I accidently brought in some damsle fly nyphms with my frogbit and duckweed.
The aphids dissapeared in a few days. The Damsel flies seemed to stay right
around the tank. I never saw them anywhere in the house.

BV.
www.iheartmypond.com